The Non-Catalytic Polymerization of Ethylene Dissolved in Naphthalene
Total Page：16
File Type：pdf, Size：1020Kb
- m THE NON-CATALYTIC POLYMERIZATION OF ETHYLENE DISSOLVED IN NAPHTHALENE by Clyde Kempton Smith A.B., Stanford University 1933 and Ben T. Woodruff B.S., University of Chicago 1932 Submitted in Partial Fulfillment of the Requirements for the degree of MASTER OF SCIENCE from the Massachusetts Institute of Technology 1935 Signatures of Authors *00 0 ~ S. Department of Chemical Engineering, July 10, 193-5 Professor in Charge of Research Chairman of Departmental Committee on Graduate Students .... .--. .. / /'j -d f I r. Massachusetts Inst. of Technology Cambridge, Mass. July 10, 1935 Professor W. G. Whitman Department of Chemical Engineering Massachusetts Institute of Technology Cambridge, Massachusetts Dear Professor Whitman: In accordance with the regulations of the Department of Chemical Engineering governing thesis work, we herewith submit a thesis entitled, "The Non- Catalytic Polymerization of Ethylene Dissolved in Naphthalenem, in partial fulfillment of the require- ments for the Master of Science Degree. Respectfully submitted, lyde Kempton Smith Ben T. Woodruff 203844 Acknowledgement The authors wish to express their gratitude to Professor Hottel for his helpful advice and counsel on the investigation of this problem. They also wish to thank Mr. F. R. Russell for his willing direction and assistance in the work. TABLE OF CONTENTS The Problem . ......... 1 Summary ...... 2 0 0 0 Introduction .... ...... 4 Previous Work by Other Investigators 5 Summary of Procedure . 0 0 0 .... .0 8 Discussion of Results . .0 * 0 .. 0 12 Conclusions . .... 0 0 0 * . ... 16 Recommendations .... .... 0 .. 0 . 0 0 0 18 Appendix Description of Apparatus .. ..... 0 0 .. 20 Procedure . * 0 0 0.. *.. 0...... 0 24 a. Operating Procedure .. 0 . .. 0 0 24 b. Analytical Procedure . 0...... 26 c. Calibrations . .. 0 .. 0 ... .. 0 31 Sample Calculations . 0 0 ... 0 ... 0 ... 34 Experimental Data Literature Cited .. .. 0 0 0 0 0 0 0 0 . 0 37 1 The purpose of this investigation was to study the polymerization of ethylene in the presence of an inert, non-catalytic hydrocarbon solvent. The solvent was to exist in a liquid phase as well as a gas phase under the conditions of reaction. Calculations were to be made to determine a constant for the rate of reaction, and some study was to be made of the products of polymeriz- ation. The problem is part of a broad program of study of the mechanism of polymerization of hydrocarbons. 2 In this investigation the primary concern was the determination of the reaction rate constant for the polymerization of ethylene dissolved in naphthalene with both liquid and gas phases present, although as a corollary the change of the constant with temperature and the nature of the products formed were also investigated. The method of finding the reaction rate constant consisted in making runs for varying lengths of time at a constant temperature of 7800 F. An indication of the change of the constant with temperature was obtained by varying the temperature while holding the time of the runs constant. By analytical means it was possible to determine the extent to which the polymerization had taken place, as well as to find in a general way the nature of the products formed. The fact that two phases were present rendered it impractical to express the ethylene concentration during the run. Another complication was the exceeding complexity of the reactions taking place in the later stages of the runs. An expression for the reaction rate constant similar in form to the second order type of reaction was obtained by plotting data on percent of original ethylene left against time of reaction. The original concentration of ethylene was about 6 mol per cent, (according to fugacity calculations). Data on the nature of the products formed indicate that hexylene is the principal gaseous olefine formed. They indicate too that certain amounts of parraffinic hydrocarbons are formed during the reaction. 4 Introduction Interest in polymerization of olefinic hydro- carbons has increased markedly in the past few years, particularly in the petroleum industry. It appears in cracking as troublesome coke and gum formation. On the other hand it is a very useful tool in the production of synthetic resins, solvents, and high grade motor fuels. Especially in connection with the latter two groups of com- pounds investigators are doing extensive work. In extending the scope of the work of polymeriza- tion of ethylene begun by Mr. Russell, it was planned to investigate the problem under conditions such that both liquid and gas phases were present. Only a very limited amount of work is reported in the literature on the non- catalytic polymerization under these conditions. Primary interest was in finding the conditions under which such polymerization would occur, in determining the reaction rate constant for the polymerization, and in gaining an indication of the change of the constant with temperature. With the limited time available it was decided to investigate the problem by arbitrarily fixing two of the four primary vari- ables, namely, the extent of the liquid phase and the initial pressure of ethylene. Runs were made at constant temperature for varying lengths of time and for varying temperature with constant lengths of time. 5 Previous Work by Other Investigators Although much work has been done on the gas phase -a polymerization of ethylene, with and without the use of catalysts, the problem of polymerization with a liquid hydrocarbon phase present has received but a limited study. A review of the literature for several years back yielded only two patents of somewhat contra- dictory nature. 2 The first one, which was issued to A. S.Ramage in 1925, states that ethylene compressed into kerosene at 00 C. and 80 lbs. per square inch pressure showed about seventy-five per cent conversion to a product which was mainly butylene. (The time of the reaction was indeter- minate from a description of the process.) He also states that higher temperatures and pressures can be used, and that the only requirement is that the ethylene dissolves in the liquid phase. Considering all the data on polymeriza- tion which requires an elevated temperature, the other patent, which was issued to H. D. Elkingtonl in 1930, seems more consistent with the facts. He states that 95 grams of ethylene heated in an autoclave with 300 grams of paraffin oil, at 45 atmospheres and 4200 C. yielded 50 grams of a light naphtha. His claims state that pure ethylene is not necessary, and that it is thus possible to use gaseous 6 cracking products oontaining ethylene, to make useful polymers. Some of the pertinent facts concerning gas- phase polymerization would be expected to apply to the liquid-phase work, at least to a certain extent; they will be discussed briefly. Ipatiev8 heated ethylene in an iron tube under high pressure, and found that polymer- ization began at 3250 C. and was quite rapid at 380 - 4000C. Hague and Wheeler, found that ethylene polymerized readily between 400 and 7000 C., yielding butylene. They used a silica bulb and heated it for three hours. According to Sachanen and Tilicheyev12 the polymerization of olefines to form higher olefines is thermodynamically possible up to 5004 C. This is brought out graphically by Francis and Kleinschmidt 5 who plotted the changes in free energy occur- ing versus the absolute temperature. The change in slope of the curve shows a tendency for ethylene to polymerize below 4250 C. and to crack at higher temperatures. Isomer- ization to cycloparaffins is possible below 4250 C. Other facts, some of which were coroborated by this investigation, are mentioned briefly below. Pressure seems to have only a small effect during the first stages of the reaction. Its main purpose is to keep the ethylene L. 7 in the liquid phase. The effects of temperature and time are similar; a short time at a high temperature shows about the same results as a long time at a lower tempera- ture. Polymerization is generally bi-molecular, or a reaction of the second order, in contrast to cracking which is a first order process. Many chain reactions may follow initial polymerization. 8 Summary-of Procedure The problem resolved itself into one of making various runs under pressure with a solvent present. Naph- thalene was used as the solvent because of its aromatic, non-cracking character, relative inactivity, and high crit- ical temperature. There were four primary variables in the experiments; they may be taken as: (1) the extent of the liquid phase; (2) the concentration of ethylene in the liquid phase; (3) temperature; and (4) time of reaction. It was obviously necessary to limit the scope of the work, and some of the variables had to be eliminated. For this reason all of the runs were made with the same liquid-gas ratio, and at the same initial concentration of ethylene. For comparison some runs were made with only the gas phase present. The required amount of naphthalene was estimated from fugacity data to give a liquid phase of about one ninth of the reactor volume. Previous work in the literature re- ported a negligible effect of pressure on the reaction, and since this determines the concentration of ethylene, the amount of ethylene originally put into the system was arbi- trarily chosen and kept constant. Runs at a constant temp- erature were made for times varying from fifteen minutes to three hours. These two variables, temperature and time, 9 were the ones mainly investigated, although a run was made to determine if the iron, of which the system mainly composed, had any catalytic effect. This was accomplished by putting steel wool in the reactor to obtain a large iron surface. The extent to which the reaction had proceeded was determined by measuring the amount of gas left after the materials had been allowed to react, and analyzing it for ethylene.